Vermont's unemployment rate stood at 3.8 in March, about where it's been since the end of 2013 and the lowest since the fall of 2006. The official unemployment rate measures unemployment by looking at people who are not working but would like to work and have been actively searching for work in the past four weeks. That means they have had job interviews, sent out resumes, called prospective employers, or engaged in similar activities to look for a job. Based on the latest measure of the state's unemployed, about 13,000 Vermonters are officially counted as unemployed.

That measure of unemployment, called the U-3 unemployment rate, is the most widely used measure of unemployment, but there are five others — some that report a lower unemployment rate and some higher. I'll ignore the measures that define and measure lower unemployment rates and focus on the higher ones because they give us the broadest picture of how many people are having a difficult time finding work.

There are some who claim that we're not really out of the recession because alternative measures of unemployment show much higher rates than the widely cited official rate. But that's not the case. If we dive deeply into the numbers, we find that all measures are down from their peaks, and most are back to pre-recession levels.

The U-4 measure includes everyone in the official U-3 measure, but it adds in people who are considered "discouraged workers." Those are people who have looked for a job sometime in the past year, but not in the past month. They have essentially given up looking for work because based on their experience, they believe that searching for a job would be futile. It could be they think they don't have enough education or training, or that they are too old or too young.

The U-4 rate last year — we don't get these alternative unemployment rates every month, as we do for the official rate — was 4.5 percent, only one-half percentage point above 2014's official U-3 rate of 4.2 percent and only slightly above where U-4 was before the recession began.

The U-5 unemployment rate includes everyone unemployed in U-4 measure and adds in "marginally attached' workers. Who are those people? They are very similar to discouraged workers, but they haven't looked for a job in the past month and don't give a reason for why they've stopped looking for work. They might have child care responsibilities, or have difficulties finding transportation to a job.

The U-5 rate last year was 5.1 percent, less than one percentage point above the U-3 rate, and also only slightly higher than it was before the Great Recession began. The U-5 measure counts a total of 17,800 people as unemployed, 3,100 more than the official measure.

The broadest measure of unemployment is the U-6 rate, which includes everyone in the U-5 measure plus all workers who are working part-time jobs but would like to work full time. That turns out to include a lot of people in Vermont.

Vermont's U-6 rate last year was 8.8 percent, more than 4 percentage points above the official rate. It is also 2 percentage points higher than it was in 2007. Out of all the different unemployment rate measures shown in the graph, U-6 is the only one that is still well above its pre-recession level.

Translating those percentages into numbers, it means that here are 13,000 Vermonters who are working at part-time jobs but would like full time employment. Given that there are 14,700 Vermonters unemployed by the official measure, that's almost as many who are unemployed by the official U-3 number.

Does that mean there is something peculiar to the Vermont economy that prevents these part-time workers from obtaining a full-time job? Possibly, but I think not.

First of all, the gap between Vermont's official unemployment rate and the U-6 rate is 4.5 percentage points. Nationally the corresponding gap is 6 percentage points, and the national U-6 rate stood at 12 percent last year. Both the gap and the level are much higher nationally than in Vermont, which suggests that the problem of part-timers looking for full-time work is even more of a problem nationally.

Second, we have to ask why so many people can't find full-time work, and the flip side of that question, why employers are unwilling to increase those workers' hours. It could be because firms don't have enough business to justify full-time work, or that businesses only need workers for a few hours a day when there are lots of customers. That's most likely the case in industries such as retailing and restaurants.

Another problem may be that many part-time employees lack the skills their employers (or other employers) need for full-time work. Or it may be that bringing the part-time employees up to full-time status would not just increase employers' wage bills, but also trigger mandatory benefit costs that are not required for part-time employees.

Whatever the reason, we know from these numbers that there are only a few thousand workers who are so discouraged by their inability to find work that they have given up looking. But the economy is expanding, and there are jobs available. The main reason for the high U-6 level of unemployment is that people are working part-time jobs and can't find full-time employment.